Suzuki Cross-coupling Catalyzed By Bridged Bis-1,2,4-triazolium Salts-palladium System

In this thesis, a series of bridged bis-1,2,4-triazolium salts were designed and synthesized, such as 4,4’-dibenzyl-1,1’-methylene-bis(1,2,4-triazolium) salt,4,4’-dibenzyl-1,1’-ethylene-bis(1,2,4-triazolium) salt,4,4’-dibenzyl-1,1’-trimethylene-bis(1,2,4-triazolium) salt,4,4’-dimethyl-1,1’-ethylene-bis(1,2,4-triazolium) salt and 4,4’-dimethyl-1,1’-trimethylene-bis(1,2,4-triazolium) salt. Catalysis performance of the bridged bis-1,2,4-triazolylidene palladium complex gernerated in situ by combination of bis-1,2,4-triazolium salt and Pd(OAc)2 in Suzuki coupling reaction was investigated. Using a model reaction of p-chloroacetophenone with phenylboronic acid, several factors, such as the base, solvent, structure of bis-1,2,4-triazolium salts and their mole ratio with palladium were optimized. The system consisting of Pd(OAc)2 and triazolium salts 4,4’-dimethyl-1,1’-ethylene-bis (1,2,4-triazolium) or 4,4’-benzyl-1,1’-ethylene-bis (1,2,4-triazolium) with 1:0.5 mole ratio showed better catalytic activity, affording the cross-coupling product in 92% and 89% yields using only 0.5% mole palladium loading while the system with longer bridge showed lower catalytic activity. Scope of the catalyst system was also investigated, showing that aryl bromides and activated aryl chlorides could be coupled with arylboronic acid smoothly.